A last-minute computer issue led to the cancellation of Boeing’s planned astronaut flight on Saturday, continuing a series of delays for the company.

The aborted launch marks another setback in Boeing’s efforts to establish itself alongside SpaceX as a reliable provider of crewed space missions for NASA.

Two NASA astronauts, Butch Wilmore and Suni Williams, were aboard the Starliner capsule when the countdown was halted by the computer system that controls the final stages of the launch.

The countdown stopped automatically at 3 minutes and 50 seconds before liftoff, leaving no time to address the problem before the launch window closed.

Technicians quickly assisted the astronauts in removing them from the capsule, which was mounted on a fully fueled Atlas V rocket at Cape Canaveral Space Force Station.

Within an hour of the launch abort, the hatch was reopened, and the astronauts were safely removed.

Tory Bruno, CEO of United Launch Alliance, the rocket’s manufacturer, explained that troubleshooting could not begin until the rocket drained its fuel.

According to Bruno, one of three redundant computers at the launch pad was functioning sluggishly, and all three must operate correctly to proceed with a launch.

Depending on the extent of the required repairs, the next launch attempt could occur as soon as Wednesday. If not, further delays until mid-June would be necessary to move the rocket off the pad and replace the batteries.

Saturday’s attempt was the second effort to launch the Starliner. The first attempt on May 6 was delayed for additional leak checks and rocket repairs.

NASA is seeking a backup to SpaceX, which has successfully flown astronauts since 2020. Boeing was initially expected to launch its first crewed mission around the same time as SpaceX. However, severe software issues during an uncrewed test flight in 2019 prevented the capsule from reaching the International Space Station (ISS).

A second test flight in 2022 was more successful, though parachute and flammability issues caused further delays. Last month, a helium leak in the capsule’s propulsion system and a recent rocket valve issue added to the challenges.

Additional valve problems surfaced two hours before Saturday’s scheduled liftoff. The team used a backup circuit to get the ground-equipment valves working to top off the rocket’s upper-stage fuel. However, the ground launch sequencer, a critical computer system, ultimately halted the launch.